JPS6045767B2 - Compressor current control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention maintains a compressor current below a predetermined maximum current value, and controls the compressor current so as to maintain it below a limit current value proportional to the outside temperature. This invention relates to a compressor current control device.

For example, in a refrigerator that cools circulating cold water, control involves adjusting the compressor vane opening depending on the temperature of the returning cold water in order to maintain the temperature of the sent out cold water at a set value. will be held.

In this control, when the vane opening increases as the chilled water temperature increases, the load on the induction motor for driving the compressor increases. There is a risk of overloading. For this reason, the current flowing through the induction motor is detected, and when the amount of current reaches the rated value of the induction motor, control is often combined to reduce the vane opening even if the cold water temperature is high. On the other hand, in order to perform cooling economically, when the outside air temperature is high, the vane opening degree is increased to increase the cooling capacity, but when the outside air temperature is low, it is necessary to control the maximum value of the vane opening degree. , thereby,
Energy savings are achieved.

This invention maintains the compressor current below a predetermined maximum current value, and even if the current is below this maximum current value, when the outside air temperature is low, maintains the compressor current below a limit current value proportional to the outside air temperature. It is an object of the present invention to provide a compressor current control device that reliably performs the following operations.

Next, an embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, the output of the current transformer is supplied between the #1 terminal and the #2 terminal. This current transformer detects the current actually supplied to the induction motor for driving the compressor of the refrigerator and generates an output current proportional to this current. The magnitude of the current supplied to the induction motor is proportional to the vane opening degree of the compressor, which changes in accordance with the magnitude of the required refrigerating capacity of the refrigerator. The output current of this current transformer is first boosted by a transformer 1, then rectified by a rectifier circuit 2 consisting of a diode bridge, and further by resistors Rl and R2.
After being smoothed by a smoothing circuit consisting of capacitors Cl and C2, it flows through a series circuit of resistor R3, variable resistor VRl, and resistor R4. The voltage V1 generated at point a at one end of this series circuit and the voltage v set by the series circuit consisting of resistor R7, variable resistor VR2, and resistor R8
% is applied to a first input of the differential amplifier U1. Therefore, basically, the differential amplifier U1
will compare the current transformer output with a reference value and generate an output VOut=Vi-v% corresponding to the difference. Here, contact 3K of relay 3K (this will be explained later)
1 is on the NC side, the voltage at point a will change depending on the settings of variable resistors VRl and VR2 if the current transformer output is constant. Ru. In this example, variable resistor VRl is set in advance at an appropriate position and then fixed, and variable resistor VR2 is set in accordance with a desired induction motor current. Assume that the voltage at point b is a value corresponding to 100% of the rated current value. This causes variable resistance VR2. The voltage V% set by the series circuit by adjusting
can be arbitrarily set within the range from 100% of the rated current value to a lower value. In this example, for convenience, it is assumed that the adjustment range of the set current value is 100% to 50%, and is set to 80%. That is, the differential amplifier U1 compares the voltage corresponding to the current transformer output with a voltage suppressed to 80% of the rated current value, and operates to generate an output voltage corresponding to the difference. Differential amplifier U1
The outputs of are simultaneously supplied to two comparison circuits 3a and 3b.

The first comparison circuit 3a detects that the output voltage of the differential amplifier U1, that is, the amount of current flowing through the induction motor of the compressor, has reached the maximum setting value by comparing it with the upper limit reference value. It operates to operate relay 1K and to disable relay 1K when the lower limit reference value is lower than the upper limit reference value. The second comparator circuit 3b also controls the relay 2K in a similar manner, except that its upper limit reference value is set to a lower value than the lower limit reference value of the first comparator circuit 3a. Relay 1K adjusts the opening of the vane of the compressor so as to reduce the opening of the vane only while the compressor is operating, and relay 2K adjusts the opening of the vane to allow the opening of the vane to increase. The contacts provided in the control circuit of the vane motor are opened and closed. The operating characteristics of relays 1K and 2K are shown in FIG. As a result, even if the cold water temperature rises and the vane attempts to open, if the current of the induction motor has reached the upper limit value, the vane will close. There is no fear that various problems will occur due to excessive current flowing through the motor.Furthermore, in this invention, the opening degree of the vane is
In addition to the magnitude of the current supplied to the induction motor,
It is also becoming limited by changes in outside temperature.

In other words, if the outside air temperature becomes low, there is no need to lower the temperature of the cold water supplied for air conditioning so much. Therefore, controlling the vane opening according to the outside air temperature is effective in eliminating wasted energy consumption due to excessive cooling and achieving energy savings. The control operation of the vane opening degree depending on the outside air temperature is performed by manually turning on the function selection switch 4 shown in FIG. 1 and turning on the photocoupler 5. Operate relay 3K through
The selection is made by switching the contact 3K1 to the NO side.

Detection of the outside air temperature is performed by a thermistor 7 connected between the #3 terminal and the #4 terminal.

The thermistor 7 includes a resistor R', a variable resistor R3, and a resistor R9.
and variable resistor VR4 to form a series circuit, and a predetermined DC voltage is applied between both ends of this series circuit.
Therefore, the voltage taken out from point d on the slider side of the variable resistor VR3 is a temperature signal corresponding to the outside temperature detected by the thermistor 7. This temperature signal is supplied to the differential amplifier U3 through the buffer amplifier U2 and compared with the voltage at point b. And the signal corresponding to the difference is
It is applied to the slider of the variable resistor VRl via the contact 3K1 which has already been switched to the NO side. In other words, at point c,
Instead of the constant voltage preset by variable resistor VR2, a temperature signal voltage that changes in response to changes in outside temperature is applied, and therefore the voltage generated at point a is:
The voltage is obtained by suppressing the current transformer output (that is, the induction motor current) according to the outside temperature. To explain this operation in more detail, the thermistor 7 has negative temperature characteristics, so if the outside temperature drops, for example, its resistance value increases, and the voltage at point d therefore decreases.

Therefore, the output voltage of buffer amplifier U2 also decreases,
Since this output is supplied to the inverting input of the differential amplifier U3, the voltage at point c corresponding to the output voltage of the differential amplifier U3 is
The lower the outside temperature, the higher it becomes. Therefore, if the current transformer output Vi is constant, the voltage at point a increases as the outside temperature decreases, and by keeping the vane opening small, the load on the induction motor decreases. .
Conversely, if the outside air temperature rises, the vane opening degree increases and the refrigeration capacity increases. The variable resistor VR3 connected in series with the thermistor 7 is used to set the ratio between the outside temperature and the voltage at point d, so that when the outside temperature is at a predetermined maximum temperature, the voltage at point a is equal to the induction motor current. It is adjusted to a value corresponding to 100%.

In this example, this 100% temperature can be adjusted within the range of 30'C to 40C. On the other hand, variable resistor VR5 inserted in the feedback circuit of differential amplifier U3 determines the amount of feedback by this feedback circuit, that is, the gain of differential amplifier U3.

By changing the resistance value of this variable resistor VR5, only the gain changes, and the 100% temperature setting value does not change. FIG. 3 is a graph showing how the relationship between the % current setting value and the outside temperature changes depending on the variable resistors VR3 and R5. Furthermore, differential amplifier U
The output voltage of 3 is applied to the comparator U4 via the resistor Rl5.
is also applied to the first input terminal of .

This comparator U4 compares the output voltage of the differential amplifier U3 with the current corresponding to the % current set value set by the variable resistor VR2, and when the former becomes lower, it The output, which was at H level until then, is changed to L level.
This turns off transistor 6 and relay 3K
becomes inoperable, its contact 3K1 is reversed, and control based on outside temperature is canceled. Resistors Rl6 and Rl7 connected between the respective terminals of the contact 3K1 are provided as a safety measure against poor contact of the contact 3K1, and their functions will be explained based on the equivalent circuit shown in FIG. 4.

Here, the resistance values of the resistors Rl6 and Rl7 are significantly larger than the resistors t/LRO and Rl5, for example, 100
It is assumed that the value of the value is selected. For example, if the contact resistance on the NC side is normal, Rl6)RO, so V″
It is % half ■%. Now, if the contact resistance on the NC side increases to infinity, if ■o=■%, then V″%=■%
And when VO<V%, V″% minus V%.Furthermore, if the contact resistance on the NC side is finite, ■″%
≦■%. That is, even if a contact failure occurs on the NC side, the voltage at point c will always be equal to or lower than the voltage % corresponding to the current setting value, and will never rise. This is the same situation as lowering the % current setting, and although the induction motor current may be limited, there is no risk of overcurrent flowing. On the other hand, if a contact failure occurs on the NO side of contact 3K1, V″O becomes equal to or lower than VO due to the same effect as described for the NC side, and this is because the outside temperature is low. It is the same state as when it was summer.Therefore, in this case as well,
・The current flowing to the induction motor is limited. As described above, according to the present invention, the operating current of the compressor is automatically limited to the lower of a preset maximum current value or a limit current value proportional to the outside temperature. This is ensured by using two differential amplifiers and one comparator.

Therefore, not only does the inconvenience of the compressor current excessively increasing beyond the set value not occur, but if the outside temperature drops, the compressor current can be limited to a corresponding limit current value. It is possible to achieve energy saving effect.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a compressor control device according to an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the operation of a relay for adjusting the vane opening, and Fig. 3 is a diagram showing the relationship between outside air temperature and % current setting value. A graph showing the relationship, FIG. 4, is an equivalent circuit diagram of a part of the circuit of FIG. 1. 1...Transformer, 2...Rectifier circuit, 3
a, 3b... Comparison circuit, 4... Contact, 5.
...Photocoupler, 6...Transistor,
7... Thermistor, 1K, 2K, 3K...
...Relay, 3K1...Contact, U1...Differential amplifier, U2...Buffer amplifier, U3...
...Differential amplifier, U4...Comparator.

Claims (1)

[Claims] 1. A current detection circuit that detects the operating current value of the compressor, first and second reference voltage generation circuits that generate first and second predetermined reference voltages, and detects outside temperature. a first differential amplifier for determining the difference between the output of the temperature detection circuit and the first reference voltage; a comparator for comparing reference voltages; a selection circuit for selecting either the output of the first differential amplifier or the second reference voltage based on the output of the comparator; and the output of the current detection circuit; a second differential amplifier for determining the difference between the output selected by the selection circuit; and a second differential amplifier for controlling the load capacity of the compressor according to the output signal of the second differential amplifier. and an output circuit that generates an output signal. 2. A compressor current control device that controls the compressor so that its operating current value is equal to or less than a predetermined maximum current value, which includes a current detection circuit that detects the operating current value of the compressor, and a current detection circuit that detects the operating current value of the compressor, and A temperature detection circuit for sensing, a reference voltage generation circuit for generating a reference voltage, a differential amplifier for calculating the difference between the reference voltage and the output of the temperature detection circuit and outputting a temperature signal voltage, and the current detection circuit. A differential amplifier circuit that takes and amplifies the difference between the output and the temperature signal voltage, and an output circuit that generates an output signal for controlling the load capacity of the compressor according to the output signal of the differential amplifier circuit. A compressor current control device comprising: